Polishing composition and method for forming wiring structure using the same

ABSTRACT

A polishing composition capable of satisfactorily polishing a semiconductor. The first polishing composition of the present invention includes silicon dioxide, at least one component selected from periodic acids and salts thereof, at least one component selected from tetraalkyl ammonium hydroxides and tetraalkyl ammonium chlorides, hydrochloric acid, and water, and contains substantially no iron. The second polishing composition of the present invention includes a predetermined amount of fumed silica, a predetermined amount of at least one component selected from periodic acids and salts thereof, a tetraalkyl ammonium salt represented by the following general formula (1), at least one component selected from ethylene glycol and propylene glycol, and water. The pH of the second polishing composition is greater than or equal to 1.8 and is less than 4.0.

FIELD OF THE INVENTION

The present invention relates to a polishing composition for use information of a wiring structure in, for example, a semiconductor device,and a method for forming a wiring structure using the polishingcomposition.

BACKGROUND OF THE INVENTION

A polishing composition for use in formation of a wiring structure in asemiconductor device is required to have a high capability for polishinga conductive metal such as tungsten and have a low capability forpolishing an insulator such as silicon dioxide. This is intended forinhibiting the occurrence of erosion on the surface of the semiconductordevice.

For forming the wiring structure, a conductor layer 13 composed of aconductive metal is generally formed on an insulator layer 11 havingtrenches 12 on the surface (see FIG. 1). Thereafter, the conductor layer13 is polished so that the insulator layer 11 in areas other thantrenches 12 is exposed (see FIG. 3). Erosion refers to a phenomenon inwhich as shown in FIG. 4, the insulator layer 11 between neighboringtrenches 12 in an area where trenches 12 are densely formed isexcessively polished, whereby the surface of the insulator layer 11 inthe area is recessed in the direction of thickness of the insulatorlayer 11 as compared to the surface of the insulator layer 11 in otherareas. The degree of recess of the surface of the insulator layer 11 atthis time is represented by erosion amount e (see FIG. 4). The erosionincreases wiring resistance of the semiconductor device and reducesflatness thereof.

Japanese Laid-Open Patent Publication No. 10-265766 discloses a firstconventional polishing composition containing hydrogen peroxide and ironnitrate. The first conventional polishing composition has a highcapability for polishing tungsten owing to a synergistic effect ofhydrogen peroxide and iron nitrate. However, iron ions originating fromiron nitrate may remain in a semiconductor device polished with thefirst conventional polishing composition. The remaining iron ions causesurface defects to occur in the semiconductor device and degradeelectrical characteristics of the semiconductor device.

On the other hand, Japanese National Phase Laid-Open Patent PublicationNo. 2000-501771 discloses a second conventional polishing compositioncontaining ammonium persulfate and potassium periodate. The secondconventional polishing composition has a high capability for polishingtungsten owing to a synergistic effect of ammonium persulfate andpotassium periodate. However, it also has a high capability forpolishing silicon dioxide. Therefore, the second conventional polishingcomposition does not inhibit erosion.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a polishing compositioncapable of satisfactorily polishing a semiconductor device.

For achieving the object described above, in one aspect of the presentinvention, the following polishing composition is provided. Thepolishing composition includes silicon dioxide, at least one componentselected from periodic acids and salts thereof, at least one componentselected from tetraalkyl ammonium hydroxides and tetraalkyl ammoniumchlorides, hydrochloric acid, and water, and contains substantially noiron.

In another aspect of the present invention, the following polishingcomposition is provided. The polishing composition includes fumed silicaat a content of greater than 20 g and less than or equal to 200 g perliter of the polishing composition; at least one component selected fromperiodic acglycol; and water. The pH of the polishing composition isgreater than or equal to 1.8 and is less than 4.0. In the generalformula (1), R¹ represents a hydrocarbon group having 1 to 4 carbonatoms, and X represents a hydroxy group or a halogen atom:

Other aspects and advantages of the present invention will be apparentfrom the following description with the drawings showing examplesembodying the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are fragmentary cross-sectional views each showing asemiconductor device in which the wiring structure is being formed usinga polishing composition according to first and second embodiments of thepresent invention;

FIG. 3 is a fragmentary cross-sectional view showing a semiconductordevice having a wiring structure formed using the polishing compositionaccording to first and second embodiments of the present invention; and

FIG. 4 is a cross-sectional view showing an enlarged part ofsemiconductor device in which erosion occurs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described below.

A polishing composition according to the first embodiment is comprisedof silicon dioxide as component A, at least one component selected fromperiodic acids and salts thereof as component B, at least one componentselected from tetraalkyl ammonium hydroxides and tetraalkyl ammoniumchlorides as component C, hydrochloric acid as component D, and water ascomponent E.

First, silicon dioxide as component A will be described.

Specific examples of silicon dioxide include colloidal silica, fumedsilica and precipitation silica. Preferable silicon dioxide is fumedsilica. Fumed silica is generally produced by subjecting silicontetrachloride to gas phase hydrolysis in an oxyhydrogen flame. Fumedsilica produced in this way has a chain structure with several toseveral tens of particles three-dimentionally agglomerated. In addition,fumed silica is characterized in that the content of metal impurities islow.

The average particle size of silicon dioxide calculated from a BETspecific surface area and a particle density is preferably 10 nm orgreater, more preferably 20 nm or greater. Furthermore, the averageparticle size is preferably 50 nm or less, more preferably 40 nm orless. Hereinafter, the average particle size calculated from the BETspecific surface area and the particle density is referred to as anaverage particle size D1. The BET specific surface area is measuredusing, for example, Flow Sorb II 2300 manufactured by Micromeritics Co.,Ltd.

The average particle size of silicon dioxide measured by alight-scattering method is preferably 80 nm or greater, more preferably100 nm or greater. Furthermore, the average particle size is preferably250 nm or less, more preferably 200 nm or less. Hereinafter, the averageparticle size measured by the light-scattering method is referred to asan average particle size D2. The average particle size D2 is measuredusing, for example, N4 Plus Submicron Particle Sizer manufactured byBeckman Coulter, Inc.

The content of silicon dioxide in the polishing composition according tothe first embodiment is preferably 20 g/liter or greater, morepreferably 50 g/liter or greater. Furthermore, the content is preferably200 g/liter or less, more preferably 150 g/liter or less.

Periodic acids and salts thereof as component B will now be described.

Specific examples of periodic acids include ortho-periodic acid (H₅IO₆),meta-periodic acid (HIO₄), bimeso-periodic acid (H₄I₂O₉), meso-periodicacid (H₃IO₅) and biortho-periodic acid (H₆I₂O₁₁). A preferable periodicacid is ortho-periodic acid. This is because ortho-periodic acid isstable in composition and can easily be obtained. Specific examples ofperiodates include various salts of the periodic acids described above.Preferable periodates are ammonium periodate, potassium periodate andsodium periodate.

The content of component B in the polishing composition according to thefirst embodiment is preferably 5 g/liter or greater, more preferably 10g/liter or greater. Furthermore, the content is preferably 50 g/liter orless, more preferably 30 g/liter or less.

Tetraalkyl ammonium hydroxides and tetraalkyl ammonium chlorides ascomponent C will now be described.

Alkyl groups of tetraalkyl ammonium hydroxides and tetraalkyl ammoniumchlorides are not specifically limited, but a methyl group or ethylgroup is preferable.

The content of component C in the polishing composition according to thefirst embodiment is preferably a content allowing the polishingcomposition to be kept at pH of 2 to 3, more preferably 2.1 to 2.8.

Hydrochloric acid as component D will now be described.

The mass fraction of hydrochloric acid in the polishing compositionaccording to the first embodiment is preferably 10 ppm or greater, morepreferably 30 ppm or greater. Furthermore, the mass fraction ispreferably 1000 ppm or less, more preferably 200 ppm or less. The massfraction, i.e. concentration, of hydrochloric acid is converted from theconcentration of chlorine measured by ion chromatography. As in the casewhere component A is fumed silica, components other than component Dcontained in the polishing composition according to the first embodimentmay contain hydrochloric acid as an impurity. In this case, if theamount of hydrochloric acid contained as an impurity is already adesired amount, it is not necessary to newly add hydrochloric acid tothe polishing composition according to the first embodiment.

Finally, water as component E will be described.

Water serves as a dispersion medium and solvent for components otherthan water contained in the polishing composition according to the firstembodiment. Preferably, as much as possible, the water contains noimpurities. Preferable water is pure water, extrapure water anddistilled water.

The components A to E described above are mixed together to prepare thepolishing composition according to the first embodiment. The pH of thepolishing composition according to the first embodiment is preferably 2or greater, more preferably 2.1 or greater. Furthermore, the pH ispreferably 3 or less, more preferably 2.8 or less.

Preferably, as much as possible, the polishing composition according tothe first embodiment contains no impurities. Specifically, the massfractions of elements of the second to twelfth groups of the periodictable, aluminum, gallium, indium, thallium, tin, lead and bismuth areeach preferably 100 ppb or less, more preferably 50 ppb or less. Copper,iron, nickel, chromium and manganese are particularly easily diffusedinto an insulator layer 11 of the semiconductor device (see FIGS. 1 to3), thus causing a reduction in yield of the semiconductor device.Therefore, it is preferable that the mass fractions of particularlycopper, iron, nickel, chromium and manganese are each within the abovedescribed range.

Expression of the number of a group of an element is based on revisedIUPAC Inorganic Chemistry Nomenclature (1989). The mass fractions, i.e.concentrations, of elements of the second to twelfth groups of theperiodic table, aluminum, gallium, indium, thallium, tin, lead andbismuth are measured using, for example, an inductively coupledplasma-mass spectroscope (ICP-MS), inductively coupled radio frequencyplasma spectroscope (ICP-AES), atomic adsorption spectrometer or TotalReflection X-ray Fluorescence analysis apparatus (TXRF).

A method for forming a wiring structure of a semiconductor device usingthe polishing composition according to the first embodiment will now bedescribed based on FIGS. 1 to 3. The method comprises a first step offorming a conductor layer 13 on an insulator layer 11 having trenches 12on the surface (see FIG. 1), a second step of polishing the conductorlayer 13 to remove most parts of the conductor layer 13 outside thetrenches 12 (see FIG. 2), and a third step of forming wiring portions 14composed of the conductor layer 13 in trenches 12 by polishing theconductor layer 13 so that the insulator layer 11 in areas other thantrenches 12 is exposed (see FIG. 3).

As shown in FIG. 1, in the first step, trenches 12 having predeterminedpatterns, i.e. grooves, based on a circuit design are first formed onthe surface of the insulator layer 11 on a semiconductor substrate (notshown). Formation of trenches 12 is performed according to a well knownlithographic technique and etching technique. Specific examples of theinsulator layer 11 include SiO₂ films such as a TEOS film, a BSG film, aPSG film and a BPSG film, a SiOF film and a SiOC film. It is desirablethat the surface of the insulator layer 11 before formation of trenches12 is as flat as possible.

After trenches 12 are formed on the insulator layer 11, the conductorlayer 13 is formed on the insulator layer 11 such that the trenches 12are at least completely filled. The conductor layer 13 is composed of aconductor metal. Specific examples of conductor metals include singlemetals such as tungsten, ruthenium, platinum, gold, hafnium, cobalt andnickel, and alloys having those single metals as bases. Because of smallwiring resistance, the conductor metal constituting the conductor layer13 is preferably tungsten, ruthenium, platinum or gold, more preferablytungsten or ruthenium, most preferably tungsten. The conductor layer 13is formed according to, for example, a PVD (Physical Vapor Deposition)method.

As shown in FIG. 2, in the second step, the conductor layer 13 formed onthe insulator layer 11 is polished with the polishing compositionaccording to the first embodiment to remove most parts of the conductorlayer 13 outside trenches 12. The term “remove most parts of theconductor layer 13 outside trenches 12” means that the conductor layer13 is removed until the thickness of the conductor layer 13 in areasoutside trenches 12 is reduced to 200 nm or less, preferably 100 nm orless.

As shown in FIG. 3, in the third step, the conductor layer 13 isfinish-polished with a finish-polishing composition described later sothat the insulator layer 11 in areas other than trenches 12 is exposed.By this finish-polishing, wiring portions 14 are formed in trenches 12,and the surface is flattened.

The finish-polishing composition for use during finish-polishing ispreferably any of first to third finish-polishing compositions describedbelow. The first finish-polishing composition is a polishing compositionsuch that when a rate at which the conductor layer 13 is polished is 1,a rate at which the insulator layer 11 is polished is in the range of0.67 to 1.5, preferably 0.75 to 1.2. The second finish-polishingcomposition is a polishing composition containing silicon dioxide ascomponent a, periodic acid as component b, at least one componentselected from ammonia, potassium hydroxide, sodium hydroxide, ammoniumperiodate, potassium periodate and sodium periodate as component c,water as component d, and containing substantially no iron. The thirdfinish-polishing composition is a polishing composition such that when arate at which the conductor layer 13 is polished is 1, a rate at whichthe insulator layer 11 is polished is in the range of 0.67 to 1.5,preferably 0.75 to 1.2, and also the polishing composition contains theabove components a to d and contains substantially no iron.

The components a to d contained in aforesaid second and thirdfinish-polishing compositions will now be described in detail.

First, silicon dioxide as component a will be described.

The type of silicon dioxide contained in the second and thirdfinish-polishing compositions is not specifically limited. Preferablesilicon dioxide is colloidal silica synthesized according to a sol-gelmethod. Synthesis of colloidal silica by the sol-gel method is generallycarried out in such a manner that methyl silicate is dropped in asolvent composed of methanol, ammonia and water, and the methyl silicateis hydrolyzed. The colloidal silica synthesized in this way ischaracterized in that the content of impurities is extremely low.

The average particle size D1 of silicon dioxide is preferably 40 nm orgreater, more preferably 60 nm or greater. Furthermore, the averageparticle size D1 is preferably 120 nm or less, more preferably 100 nm orless. The average particle size D2 is preferably 80 nm or greater, morepreferably 150 nm or greater. Furthermore, the average particle size D2is preferably 300 nm or less, more preferably 250 nm or less.

The content of silicon dioxide in the second and third finish-polishingcompositions is preferably 10 g/liter or greater, more preferably 30g/liter or greater. Furthermore, the content is preferably 200 g/literor less, more preferably 150 g/liter or less.

The periodic acid as component b will now be described. The content ofperiodic acid in the second and third finish-polishing compositions ispreferably 2 g/liter or greater, more preferably 3.5 g/liter or greater.Furthermore, the content is preferably 9 g/liter or less, morepreferably 6 g/liter or less.

Ammonia, potassium hydroxide, sodium hydroxide, ammonium periodate,potassium periodate and sodium periodate as component c will now bedescribed. The content of component c in the second and thirdfinish-polishing compositions is preferably a content allowing thepolishing composition to be kept at a pH of 4.5 to 7, more preferably 5to 6, most preferably 5.3 to 5.8.

Finally, water as component d will be described. Water serves as adispersion medium and solvent for components other than water containedin the second and third finish-polishing compositions. Preferably, asmuch as possible, the water contains no impurities. Preferable water ispure water, extrapure water and distilled water.

Other components are optionally added to the above components a to d toprepare the second and third finish-polishing compositions.

The pH of the finish-polishing composition is preferably 4.5 or greater,more preferably 5 or greater, most preferably 5.3 or greater.Furthermore, the pH is preferably 7 or less, more preferably 6 or less,most preferably 5.8 or less.

Preferably, as much as possible, the finish-polishing compositioncontains no impurities as much as possible. Specifically, the massfractions of elements of the second to twelfth groups of the periodictable, aluminum, gallium, indium, thallium, tin, lead and bismuth areeach preferably 100 ppb or less, more preferably 50 ppb or less. Copper,iron, nickel, chromium and manganese are particularly easily diffusedinto the insulator layer 11, thus causing a reduction in yield of thesemiconductor device. Therefore, it is preferable that the massfractions of particularly copper, iron, nickel, chromium and manganeseare each within the above described range.

The first embodiment has the following advantages.

The polishing composition according to the first embodiment is comprisedof silicon dioxide, at least one component selected from periodic acidsand salts thereof, at least one component selected from tetraalkylammonium hydroxides and tetraalkyl ammonium chlorides, hydrochloric acidand water, and contains substantially no iron. Thus, no iron ions remainin a semiconductor device polished with the polishing compositionaccording to the first embodiment. Therefore, there is no possibilitythat defects occur on the surface of the semiconductor device due tocontamination by iron, or electrical characteristics of thesemiconductor device are degraded.

The polishing composition according to the first embodiment has a highcapability for polishing the conductor layer 13, especially theconductor layer 13 made of tungsten, owing to a synergic effect ofmechanical polishing action of silicon dioxide and chemical polishingaction of at least one component selected from periodic acids and saltsthereof and hydrochloric acid. In other words, the polishing compositionaccording to the first embodiment has a capability for polishing at ahigh rate the conductor layer 13, especially the conductor layer 13 madeof tungsten. The reason why the polishing composition according to thefirst embodiment has a high capability for polishing tungsten is that atleast one component selected from periodic acids and salts thereofchanges tungsten into tungsten trioxide by oxidation action. Tungstentrioxide is so brittle that it can easily be removed by mechanicalpolishing action of silicon dioxide.

The tetraalkyl ammonium hydroxide or tetraalkyl ammonium chloridecontained in the polishing composition according to the first embodimentlowers the capability for polishing the insulator layer 11 by thepolishing composition according to the first embodiment. Therefore,polishing of the insulator layer 11 is inhibited during formation of awiring structure for the semiconductor device.

If silicon dioxide contained in the polishing composition according tothe first embodiment is fumed silica, a polishing composition isprovided having a high capability for polishing the conductor layer 13and a low capability for polishing the insulator layer 11, in otherwords, a polishing composition is provided having an increased rate atwhich the conductor layer is polished and a reduced rate at which theinsulator layer is polished. This is inferred to be ascribable to aunique form of fumed silica in which a chain structure is formed withseveral to several tens of particles three-dimentionally agglomerated.

If the average particle size D1 of silicon dioxide contained in thepolishing composition according to the first embodiment is 10 nm orgreater, a polishing composition is provided having an increased rate atwhich a conductive layer is polished. If the average particle size D1 is20 nm or greater, the rate at which the conductor layer is polished isstill further increased.

If the average particle size D1 of silicon dioxide contained in thepolishing composition according to the first embodiment is 50 nm orless, a polishing composition is provided having a reduced rate at whichan insulator layer is polished. If the average particle size D1 is 40 nmor less, the rate at which the insulator layer is polished is stillfurther reduced.

If the average particle size D2 of silicon dioxide contained in thepolishing composition according to the first embodiment is 80 nm orgreater, a polishing composition is provided having an increased rate atwhich a conductive layer is polished. If the average particle size D2 is100 nm or greater, the rate at which the conductor layer is polished isstill further increased.

If the average particle size D2 of silicon dioxide contained in thepolishing composition according to the first embodiment is 250 nm orless, a polishing composition is provided having a reduced rate at whichan insulator layer is polished. If the average particle size D2 is 200nm or less, the rate at which the insulator layer is polished is stillfurther reduced.

If the content of silicon dioxide contained in the polishing compositionaccording to the first embodiment is 20 g/liter or greater, a polishingcomposition is provided having an increased rate at which a conductivelayer is polished. If the content is 50 g/liter or greater, the rate atwhich the conductor layer is polished is still further increased.

If the content of silicon dioxide contained in the polishing compositionaccording to the first embodiment is 200 g/liter or less, a polishingcomposition is provided having a reduced rate at which an insulatorlayer is polished. If the content is 150 g/liter or less, the rate atwhich the insulator layer is polished is still further reduced.

If the content of component B (at least one component selected fromperiodic acids and salts thereof) in the polishing composition accordingto the first embodiment is 5 g/liter or greater, a polishing compositionis provided having an increased rate at which a conductor layer ispolished. If the content is 10 g/liter or greater, the rate at which theconductor layer is polished is still further increased.

If the content of component B in the polishing composition according tothe first embodiment is 50 g/liter or less, a polishing composition isprovided having a reduced rate at which an insulator layer is polished.If the content is 30 g/liter or less, the rate at which the insulatorlayer is polished is still further reduced.

If the mass fraction of hydrochloric acid in the polishing compositionaccording to the first embodiment is 10 ppm or greater, a polishingcomposition is provided having an increased rate at which a conductorlayer is polished and a reduced rate at which an insulator layer ispolished. If the mass fraction is 30 ppm or greater, the rate at whichthe conductor layer is still further increased, and the rate at whichthe insulator layer is still further reduced.

If the mass fraction of hydrochloric acid in the polishing compositionaccording to the first embodiment is 1000 ppm or less, gelation of thepolishing composition according to the first embodiment is prevented. Ifthe mass fraction is 200 ppm or less, the gelation is reliablyprevented. The gelated polishing composition according to the firstembodiment causes polishing scars to occur on the polished surface.

If the pH of the polishing composition according to the first embodimentis 2 or greater, a polishing composition is provided having an increasedrate at which a conductor layer is polished and a reduced rate at whichan insulator layer is polished. In addition, handling characteristics ofthe polishing composition according to the first embodiment areimproved. If the pH is 2.1 or greater, the rate at which the conductorlayer is polished is still further increased, and the rate at which theinsulator layer is polished is still further reduced.

If the pH of the polishing composition according to the first embodimentis 3 or less, gelation of the polishing composition according to thefirst embodiment is prevented. If the pH is 2.8 or less, the gelation isreliably prevented.

If the mass fractions of elements of the second to twelfth groups of theperiodic table, aluminum, gallium, indium, thallium, tin, lead andbismuth in the polishing composition according to the first embodimentare each 100 ppb or less, contamination of the semiconductor device bythese elements is inhibited. If the mass fraction is 50 ppb or less, thecontamination is considerably inhibited. Contamination of thesemiconductor device by aluminum and the like causes occurrence ofsurface defects and degradation in electrical characteristics.

If finish-polishing is performed using a polishing composition such thatwhen a rate at which the conductor layer is polished is 1, a rate atwhich the insulator layer is polished is in the range of 0.67 to 1.5,the conductor layer and the insulator layer are polished at almost thesame rates, and therefore a flat finished surface is obtained. Iffinish-polishing is performed using a polishing composition such thatwhen a rate at which the conductor layer is polished is 1, a rate atwhich the insulator layer is polished is in the range of 0.75 to 1.2,and the flatness of the finished surface is still further improved.

If finish-polishing is performed using a finish-polishing compositioncontaining the above components a to d and containing substantially noiron, contamination of the semiconductor by iron is prevented.

If finish-polishing is performed using a polishing composition such thatwhen a rate at which the conductor layer is polished is 1, a rate atwhich the insulator layer is polished is in the range of 0.67 to 1.5,and the finish-composition contains the above components a to d andcontains substantially no iron, a flat finished surface is obtained, andalso contamination by iron is prevented.

If the average particle size D1 of silicon dioxide contained in thefinish-polishing composition is 40 nm or greater, a finish-polishingcomposition is provided having an increased rate at which a conductorlayer is polished and also an increased rate at which an insulator layeris polished. If the average particle size D1 is 60 nm or greater, therate at which the conductor layer is polished and the rate at which theinsulator layer is polished are still further increased.

If the average particle size D1 of silicon dioxide contained in thefinish-polishing composition is 120 nm or less, the finish-polishingcomposition has an adequate viscosity, and dispersibility of silicondioxide is improved. If the average particle size D1 is 100 nm or less,dispersibility of silicon dioxide is still further improved. Poordispersibility of silicon dioxide causes polishing scars to occur on thepolished surface.

If the average particle size D2 of silicon dioxide contained in thefinish-polishing composition is 80 nm or greater, a finish-polishingcomposition is provided having an increased rate at which a conductorlayer is polished and an increased rate at which an insulator layer ispolished. If the average particle size D2 is 150 nm or greater, the rateat which the conductor layer is polished and the rate at which theinsulator layer is polished are still further increased.

If the average particle size D2 of silicon dioxide contained in thefinish-polishing composition is 300 nm or less, the finish-polishingcomposition has an adequate viscosity, and dispersibility of silicondioxide is improved. If the average particle size D2 is 250 nm or less,dispersibility of silicon dioxide is still further improved.

If the content of silicon dioxide contained in the finish-polishingcomposition is 10 g/liter or greater, a finish-polishing composition isprovided having an increased rate at which a conductor layer is polishedand an increased rate at which an insulator layer is polished. If thecontent is 30 g/liter or greater, the rate at which the conductor layeris polished and the rate at which the insulator layer is polished arestill further increased.

If the content of silicon dioxide contained in the finish-polishingcomposition is 200 g/liter or less, the finish-polishing composition hasan adequate viscosity, and dispersibility of silicon dioxide isimproved. If the content is 150 g/liter or less, dispersibility ofsilicon dioxide is still further improved.

If the content of periodic acid in the finish-polishing composition is 2g/liter or greater, a finish-polishing composition is provided having anincreased rate at which a conductor layer is polished and an increasedrate at which an insulator layer is polished. If the content is 3.5g/liter or greater, the rate at which the conductor layer is polishedand the rate at which the insulator layer is polished are still furtherincreased.

If the content of periodic acid in the finish-polishing composition is 9g/liter or less, the finish-polishing composition has adequate oxidationpower. If the content is 6 g/liter or less, it has a more adequateoxidation power.

If the pH of the finish-polishing composition is 4.5 or greater, afinish-polishing composition is provided having an increased rate atwhich a conductor layer is polished. If the pH is 5 or greater, the rateat which the conductor layer is polished is further increased, and ifthe pH is 5.3 or greater, the rate at which the conductor layer ispolished is still further increased.

If the pH of the finish-polishing composition is 7 or less, afinish-polishing composition is provided having an increased rate atwhich an insulator layer is polished is provided. If the pH is 6 orless, the rate at which the insulator layer is polished is furtherincreased, and if the pH is 5.8 or less, the rate at which the insulatorlayer is polished is still further increased.

If the mass fractions of elements of the second to twelfth groups of theperiodic table, aluminum, gallium, indium, thallium, tin, lead andbismuth in the finish-polishing composition are each 100 ppb or less,contamination of the semiconductor device by these elements isinhibited. If the mass fraction is 50 ppb or less, the contamination isconsiderably inhibited.

A second embodiment of the present invention will be described below.

A polishing composition according to the second embodiment is comprisedof fumed silica as component A′, at least one component selected fromperiodic acids and salts thereof as component B′, a tetraalkyl ammoniumsalt represented by the general formula (1) described below as componentC′, at least one component selected from ethylene glycol and propyleneglycol as component D′, and water as component E′, ammonium nitrate asF′ component, and at least one component selected from benzotriazole andderivatives thereof as G′:

R¹ in the general formula (1) represents a hydrocarbon group having 1 to4 carbon atoms, and X represents a hydroxy group or a halogen atom.

The average particle size D1 of fumed silica as component A′ ispreferably 10 to 50 nm, more preferably 20 to 40 nm. The averageparticle size D2 of fumed silica is preferably 80 to 250 nm, morepreferably 100 to 200 nm. If the average particle size D1 is less than10 nm or the average particle size D2 is less than 80 nm, the rate atwhich a conductor layer is polished is insufficient. If the averageparticle size D1 is greater than 50 nm or the average particle size D2is greater than 250 nm, the rate at which an insulator layer is polishedis so high that erosion amount increases.

It is essential that the content of fumed silica in the polishingcomposition according to the second embodiment is greater than 20g/liter and also 200 g/liter or less, and is preferably 50 to 100g/liter. If the content is 20 g/liter or less, the rate at which theconductor layer is polished is insufficient, thus increasing the amountof polishing time. An increase in the amount of polishing time causesthe erosion amount to be increased. If the content is greater than 200g/liter, the viscosity is excessively increased to make handlingdifficult, and storage stability is lowered.

A periodic acid preferable as component B′ is ortho-periodic acid.Periodates preferable as component B′ are ammonium periodate, potassiumperiodate and sodium periodate.

It is essential that the content of component B′ in the polishingcomposition according to the second embodiment be greater than 5 g/literand also 25 g/liter or less, and is preferably 7.5 to 17.5 g/liter. Ifthe content is 5 g/liter or less, the rate at which the conductor layeris polished is insufficient, thus increasing the amount of polishingtime. If the content is greater than 25 g/liter, the rate at which theinsulator layer is polished increases, resulting in an increase inerosion amount.

Component C′ reduces the rate at which the insulator layer is polishedby the polishing composition according to the second embodiment.Specific examples of the hydrocarbon group R₁ having 1 to 4 carbon atomsin the tetraalkyl ammonium salt represented by the general formula (1)described above include saturated hydrocarbon groups, unsaturatedhydrocarbon groups, straight-chain hydrocarbon groups and branchedhydrocarbon groups. A preferable hydrocarbon group R₁ is astraight-chain saturated hydrocarbon group having less than 3 carbonatoms, specifically a methyl group and an ethyl group.

The content of component C′ in the polishing composition according tothe second embodiment is preferably a content allowing the polishingcomposition to be kept at pH of 1.8 or greater to less than 4.0, morepreferably 2.0 to 3.0.

Ethylene glycol and propylene glycol inhibit excessive chemical actionon the conductor layer 13, and prevents the conductor layer 13 in thetrenches 12 from being polished. If the conductor layer 13 in thetrenches 12 is polished, polishing pressure is focused on the surface ofthe insulator layer 11 between neighboring trenches 12, and thereforethe erosion amount is increased. On the other hand, polyethylene glycoland polypropylene glycol have an extremely strong effect of inhibitingchemical action on the conductor layer 13. Thus, a polishing compositioncontaining polyethylene glycol and polypropylene glycol instead ofethylene glycol and propylene glycol has an insufficient rate at whichthe conductor layer is polished.

The content of component D′ in the polishing composition according tothe second embodiment is preferably 0.03 to 2.0 g/liter, more preferably0.08 to 1.0 g/liter. If the content is less than 0.03 g/liter, theeffect of inhibiting excessive chemical action on the conductor layer 13is insufficient, resulting in an increase in erosion amount. Inaddition, surface defects may occur on a polished surface. If thecontent is greater than 2.0 g/liter, storage stability is degraded,resulting in occurrence of precipitation and separation.

Water as component E′ serves as a dispersant and solvent for componentsother than water contained in the polishing composition according to thesecond embodiment. Preferably, as much as possible, the water containsno impurities. Preferable water is pure water, extrapure water anddistilled water.

Ammonium nitrate as F′ component facilitates chemical polishing actionof component B′ to improve the rate at which the conductor layer ispolished by the polishing composition according to the secondembodiment. The content of ammonium nitrate in the polishing compositionaccording to the second embodiment is preferably 5 to 30 g/liter, morepreferably 10 to 25 g/liter. If the content is less than 5 g/liter, therate at which the conductor is polished is not sufficiently improved. Ifthe content is greater than 30 g/liter, the rate at which the conductorlayer is polished is so high that surface defects may occur on thepolished surface.

Benzotriazole and derivatives thereof as G′ component protect thesurface of the conductor layer 13 to prevent corrosion of the conductorlayer 13. Benzotriazole is more effective in protecting the surface ofthe conductor layer 13 than benzotriazole derivatives. Benzotriazole andderivatives thereof are each represented by the general formuladescribed below (2):

R² in the general formula (2) represents an alkyl group such as an alkylgroup containing a carboxyl group, an alkyl group containing a hydroxygroup and a tertiary amino group and an alkyl group containing a hydroxygroup, or a hydrogen atom. R³ to R⁶ each represent a hydrogen atom or analkyl group. The carbon atom at the fourth, fifth, sixth or seventhposition may be replaced with a nitrogen atom. The nitrogen atom at thefirst position may be replaced with a carbon atom.

The content of G′ component in the polishing composition according tothe second embodiment is preferably 0.05 to 3.5 g/liter, more preferably0.15 to 1.5 g/liter. If the content is less than 0.05 g/liter, theeffect of protecting the surface of the conductor layer 13 isinsufficient. If the content is greater than 3.5 g/liter, the surface ofthe conductor layer 13 is excessively protected, and thus the rate atwhich the conductor layer is polished becomes insufficient. In addition,dissolution stability of the G′ component is degraded, resulting inoccurrence of precipitation and separation.

The A′ to G′ components are mixed to prepare the polishing compositionaccording to the second embodiment. The pH of the polishing compositionaccording to the second embodiment should be 1.8 or greater to less than4.0, and is preferably 2.0 to 3.0. If the pH is less than 1.8, the rateat which the insulator layer is polished becomes so high that theerosion amount is increased and in addition, handling characteristicsare lowered. If the pH is 4.0 or greater, the rate at which theinsulator layer is polished becomes so high that the erosion amount isincreased. In addition, dispersion stability is degraded, resulting inoccurrence of separation and gelation.

Preferably, the polishing composition according to the second embodimentcontains no impurities as much as possible. Specifically, the massfractions of elements of the second to twelfth groups of the periodictable, aluminum, gallium, indium, thallium, tin, lead and bismuth areeach preferably 100 ppb or less, more preferably 50 ppb or less. Copper,iron, nickel, chromium and manganese are particularly easily diffusedinto the insulator layer 11 of the semiconductor device, thus causing areduction in yield of the semiconductor device. Therefore, it ispreferable that the mass fractions of particularly copper, iron, nickel,chromium and manganese are each within the above described range.

The content of chlorine contained as an impurity in fumed silica ascomponent A′ is preferably a content allowing the mass fraction ofchlorine in the polishing composition according to the second embodimentto be kept at a 1,000 ppm or less, more preferably 200 ppm or less. Ifthe mass fraction is greater than 1,000 ppm, stability of the polishingcomposition according to the second embodiment is degraded, resulting inoccurrence of gelation.

The rate at which the conductor layer is polished by the polishingcomposition according to the second embodiment is preferably 200 to 500nm/min, more preferably 300 to 400 nm/min. If the polishing rate is lessthan 200 nm/min, the amount of polishing time increases. If thepolishing rate is greater than 500 nm/min, it is difficult to maintainthe polishing rate with stability.

The polishing composition according to the second embodiment is used information of a wiring structure in a semiconductor device. The methodfor forming the wiring structure using the polishing compositionaccording to the second embodiment is same as the method for forming thewiring structure using the polishing composition according to the firstembodiment.

The polishing composition according to the second embodiment has a highcapability for polishing the conductor layer 13, especially theconductor layer 13 made of tungsten, owing to a synergic effect ofmechanical polishing action of silicon dioxide and chemical polishingaction of at least one component selected from periodic acids and saltsthereof. On the other hand, the polishing composition according to thesecond embodiment has a reduced capability for polishing the insulatorlayer 11 due to a synergic effect of action of a tetraalkyl ammoniumsalt represented by the general formula (1), and action of a pH set tobe 1.8 or greater to less than 4.0. Thus, in a semiconductor devicepolished with the polishing composition according to the secondembodiment, erosion is inhibited to reduce the erosion amount.

The first and second embodiments may be altered as follows.

The polishing composition according to the first and second embodimentsmay contain various kinds of additives that are generally used inconventional polishing compositions, such as an anti-forming agent, forexample.

The polishing composition according to the second embodiment is notnecessarily required to contain both the F′ component and G′ component.

In the method for forming a wiring structure according to the firstembodiment, a finish-polishing composition is used in the third step,but the polishing composition according to the first embodiment may beused instead of the finish-polishing composition. That is, only thepolishing composition according to the first embodiment may be used topolish the conductor layer 13 so that the insulator layer 11 in areasother than trenches 12 is exposed.

In the method for forming a wiring structure according to the secondembodiment, a finish-polishing composition is used in the third step,but the polishing composition according to the second embodiment may beused instead of the finish-polishing composition. That is, only thepolishing composition according to the second embodiment may be used topolish the conductor layer 13 so that the insulator layer 11 in areasother than trenches 12 is exposed.

In the method for forming a wiring structure according to the first andsecond embodiments, the conductor layer 13 is formed directly on theinsulator layer 11. In contrast, a primary coat composed of titanium ortitanium nitrate may be formed on the insulator layer 11, followed byforming the conductor layer 13 on the primary coat. That is, a metallayer comprised of the primary coat and the conductor layer 13 may beformed on the insulator layer 11 having trenches 12 on the surface. Inthis case, in the third step, the metal layer is polished so that theinsulator layer 11 in areas other than trenches 12 is exposed, wherebywiring portions 14 are formed. The primary coat prevents the conductorlayer 13, hence the wiring portions 14 from being peeled off from theinsulator layer 11.

The polishing composition and finish-polishing composition according tothe first and second embodiments may be provided in the form of amultiple agent system comprised of two or more agents that are mixedwhen used. The polishing component according to the first embodiment maybe provided in the form of a double agent system comprised of a firstagent containing component A, component D and component E and a secondagent containing component B, component C and component E, for example.The polishing composition according to the second embodiment may beprovided in the form of a double agent system comprised of a first agentcontaining component A′ and component E′ and a second agent containingcomponent B′, component C′, component D′ and component E′, for example.The finish-polishing component may be provided in the form a doubleagent system comprised of a first agent containing component a andcomponent d and a second agent containing component b, component c andcomponent d, for example. This improves storage stability. In addition,by adjusting the mixing ratio of the agents according to the state of apolisher and environments during polishing, the polishing rate can befinely adjusted.

The polishing composition according to the first and second embodimentsmay be provided as a concentrated stock solution. In this case, thepolishing composition according to the first and second embodiments isdiluted with water when used for polishing. This improves handlingcharacteristics during storage and transportation.

EXAMPLES

The present invention will now be more specifically described withExamples and Comparative Examples.

Examples 1 to 26 and Comparative Examples 1 to 5

In Examples 1 to 24, fumed silica, periodic acid, hydrochloric acid,tetramethyl ammonium hydroxide and water were mixed to prepare apolishing composition. In Example 25, fumed silica, periodic acid,potassium periodate, hydrochloric acid, tetramethyl ammonium hydroxideand water were mixed to prepare a polishing composition. In Example 26,colloidal silica, periodic acid, hydrochloric acid, tetramethyl ammoniumhydroxide and water were mixed to prepare a polishing composition. InComparative Example 1, fumed silica, hydrochloric acid, tetramethylammonium hydroxide and water were mixed to prepare a polishingcomposition. In Comparative Example 2, fumed silica, periodic acid,tetramethyl ammonium hydroxide and water were mixed to prepare apolishing composition. In Comparative Example 3, fumed silica, periodicacid, hydrochloric acid and water were mixed to prepare a polishingcomposition. In Comparative Example 4, fumed silica, periodic acid,hydrochloric acid, potassium hydroxide and water were mixed to prepare apolishing composition. In Comparative Example 5, fumed silica, ironnitrate, hydrochloric acid, tetramethyl ammonium hydroxide and waterwere mixed to prepare a polishing composition.

The contents of fumed silica and periodic acid and the mass fractions ofchlorine in polishing compositions prepared in Examples 1 to 26 andComparative Examples 1 to 5, and the pHs of the polishing compositionsare shown in Table 1 below. The contents of tetramethyl ammoniumhydroxide in polishing compositions prepared in Examples and ComparativeExamples other than Comparative Examples 3 and 4, and the content ofpotassium hydroxide in the polishing composition prepared in ComparativeExample 4 are contents allowing the pHs of the respective polishingcompositions to have the values shown in Table 1. The average particlesize D1 and the average particle size D2 of fumed silica contained inthe polishing compositions prepared in Examples 1 to 25 and ComparativeExamples 1 to 5 are 30 nm and 100 nm, respectively.

Examples 27 to 39

In Examples 27 to 29, fumed silica, periodic acid, hydrochloric acid,tetramethyl ammonium hydroxide and water were mixed to prepare apolishing composition. The average particle size D1 and the averageparticle size D2 of fumed silica contained in the polishing compositionsprepared in Examples 27 to 39 are shown in Table 2. The content of fumedsilica in polishing compositions prepared in Examples 27 to 39 is 100gAiter, the content of periodic acid is 20 g/liter, the mass fraction ofchlorine is 100 ppm, and the content of tetramethyl ammoniun hydroxideis a content allowing the polishing composition to be kept at pH of 2.3.

Using polishing compositions prepared in Examples 1 to 39 andComparative Examples 1 to 5, a blanket wafer of tungsten and a blanketwafer of SiO₂ were polished for 1 minute in accordance with polishingconditions (1) described below. At this time, the tungsten polishingrate and the SiO₂ polishing rate of each polishing composition wasdetermined based on the equation described below. In addition, theconcentration of iron ion on the surface of each polished wafer witheach polishing composition was measured using Total Reflection X-rayFluorescence analyzer (TRE-610T manufactured by Technos Co., Ltd.). Theresults are shown in Tables 1 and 2.Polishing rate [nm/min]=(thickness [nm] of non-polished blanketwafer−thickness [nm] of polished blanket wafer)÷polishing time [min]

The thicknesses of the blanket wafer of tungsten before and afterpolishing were measured using a sheet resistance measuring apparatus(VR-120 manufactured by International Electric System Service Co.,Ltd.). The thickness of the blanket wafer of SiO₂ before and afterpolishing were measured using an optical film thickness measuringapparatus manufactured by Dainippon Screen Manufacture Co., Ltd.

Polishing Conditions (1)

Polisher: polisher for one side CMP (Mirra manufactured by AppliedMaterials Co., Ltd.); polishing pad: laminated polishing pad made ofpolyurethane (IC-1000/Suba 400 manufactured by Rodel Co., Ltd.);polishing pressure: 4 psi (=28 kPa), platen speed: 80 rpm, rate of feedof polishing composition: 150 ml/minute, carrier speed: 80 rpm.

TABLE 1 Tungsten SiO₂ Concentration of Fumed Periodic polishingpolishing iron ion on the silica acid Chlorine rate rate surface ofwafer (g/L) (g/L) (ppm) pH (nm/min) (nm/min) Atms/cm² Ex. 1 10 20 1002.3 250 3 <1 × 10¹⁰ Ex. 2 20 20 100 2.3 270 3.5 <1 × 10¹⁰ Ex. 3 50 20100 2.3 320 4.5 <1 × 10¹⁰ Ex. 4 100 20 100 2.3 380 6 <1 × 10¹⁰ Ex. 5 15020 100 2.3 395 8 <1 × 10¹⁰ Ex. 6 200 20 100 2.3 410 10 <1 × 10¹⁰ Ex. 7250 20 100 2.3 420 13 <1 × 10¹⁰ Ex. 8 100 3 100 2.3 120 6 <1 × 10¹⁰ Ex.9 100 5 100 2.3 180 6 <1 × 10¹⁰ Ex. 10 100 10 100 2.3 270 6.5 <1 × 10¹⁰Ex. 11 100 30 100 2.3 410 8 <1 × 10¹⁰ Ex. 12 100 50 100 2.3 420 9 <1 ×10¹⁰ Ex. 13 100 80 100 2.3 440 10 <1 × 10¹⁰ Ex. 14 100 20 5 2.3 350 9 <1× 10¹⁰ Ex. 15 100 20 10 2.3 360 9 <1 × 10¹⁰ Ex. 16 100 20 30 2.3 375 8<1 × 10¹⁰ Ex. 17 100 20 200 2.3 385 6 <1 × 10¹⁰ Ex. 18 100 20 1000 2.3395 4 <1 × 10¹⁰ Ex. 19 100 20 2000 2.3 420 2 <1 × 10¹⁰ Ex. 20 100 20 1001.8 255 10 <1 × 10¹⁰ Ex. 21 100 20 100 2.0 340 9.5 <1 × 10¹⁰ Ex. 22 10020 100 2.1 350 9 <1 × 10¹⁰ Ex. 23 100 20 100 2.8 380 8 <1 × 10¹⁰ Ex. 24100 20 100 3.0 400 8 <1 × 10¹⁰ Ex. 25 ^(Note1) 100 10 100 2.3 370 8 <1 ×10¹⁰ Ex. 26 ^(Note2) — 20 100 2.3 250 80 <1 × 10¹⁰ C. Ex. 1 100 — 1002.3 20 5 <1 × 10¹⁰ C. Ex. 2 100 20 — 2.3 280 11 <1 × 10¹⁰ C. Ex. 3 10020 100 1.5 240 30 <1 × 10¹⁰ C. Ex. 4 100 20 100 2.3 240 80 <1 × 10¹⁰ C.Ex. 5 ^(Note3) 100 — 100 2.3 400 7  3 × 10¹² ^(Note1): The polishingcomposition of Example 25 further contains 10 g/L of potassiumperiodate. ^(Note2): The polishing composition of Example 26 furthercontains 100 g/L of colloidal silica. ^(Note3): The polishingcomposition of Comparative Example 5 further contains 20 g/L of ironnitrate.

TABLE 2 SiO₂ Concentration of Tungsten polishing iron ion on the D1 D2polishing rate rate surface of wafer (nm) (nm) (nm/min) (nm/min)Atms/cm² Ex. 27 7 100 200 1.5 <1 × 10¹⁰ Ex. 28 10 100 250 2 <1 × 10¹⁰Ex. 29 20 100 320 4 <1 × 10¹⁰ Ex. 30 30 100 380 6 <1 × 10¹⁰ Ex. 31 40100 385 8 <1 × 10¹⁰ Ex. 32 50 100 390 10 <1 × 10¹⁰ Ex. 33 70 100 400 12<1 × 10¹⁰ Ex. 34 30 40 320 4 <1 × 10¹⁰ Ex. 35 30 50 340 4.5 <1 × 10¹⁰Ex. 36 30 80 360 5 <1 × 10¹⁰ Ex. 37 30 150 400 6.5 <1 × 10¹⁰ Ex. 38 30200 405 7.5 <1 × 10¹⁰ Ex. 39 30 250 410 8 <1 × 10¹⁰

As shown in Tables 1 and 2, polishing compositions of Examples 1 to 39had increased tungsten polishing rates compared to the polishingcomposition of Comparative Example 1 containing no periodic acid.Polishing compositions of Examples 1 to 39 had less concentrations ofiron ion on the surface of the polished wafer compared to the polishingcomposition of Comparative Example 5 containing iron nitrate. Thepolishing composition of Comparative Example 2 containing nohydrochloric acid and polishing compositions of Comparative Examples 3and 4 containing no tetramethyl ammonium hydroxide had reduced tungstenpolishing rates and increased SiO₂ polishing rates.

Examples 40 to 58

In Examples 40 to 58, a pattern wafer was polished for 1 minute inaccordance with the above polishing conditions (1) using the polishingcomposition prepared in Example 4, and then finish-polished using afinish-polishing composition in accordance with the polishing conditions(2) described below. Alter the pattern wafer was finish-polished, theamount of dishing and the amount of erosion in an area of the patternwafer having a density of 50% and a hole diameter of 1 μm, namely thearea of the pattern wafer on which wiring portions relatively densely,where measured. The results are shown in Table 3 below. Thefinish-polishing composition used in each Example was prepared by mixingcolloidal silica, periodic acid, ammonia and water. The contents ofcolloidal silica and periodic acid in the finish-polishing compositionand the pH of the finish-polishing are shown in Table 3 below. Inaddition, the tungsten polishing rate and SiO₂ polishing rate of thefinish-polishing composition used in each Example and the ratio of thepolishing rates (SiO₂ polishing rate/tungsten polishing rate) are shownin Table 3 below. relatively densely, were measured. The results areshown in Table 3 below. The finish-polishing composition used in eachExample was prepared by mixing colloidal silica, periodic acid, ammoniaand water. The contents of colloidal silica and periodic acid in thefinish-polishing composition and the pH of the finish-polishing areshown in Table 3 below. In addition, the tungsten polishing rate andSiO₂ polishing rate of the finish-polishing composition used in eachExample and the ratio of the polishing rates (SiO₂ polishingrate/tungsten

Polishing Conditions (2)

Polisher: polisher for one side CMP (Mirra manufactured by AppliedMaterials Co., Ltd.); polishing pad: composite polishing pad made ofpolyurethane (IC-1000/Suba 400 manufactured by Rodel Co., Ltd.);polishing pressure: 4 psi (=28 kPa), polishing time: 60 seconds, platenspeed: 60 rpm, rate of feed of polishing composition: 200 ml/minute,carrier speed: 60 rpm.

TABLE 3 Tungsten SiO₂ Colloidal Periodic polishing polishing Ratio ofsilica acid rate rate polishing Dishing Erosion (g/L) (g/L) pH (nm/min)(nm/min) rates (nm) (nm) Ex. 40 7 4 5.5 27 35 1.30 1 12 Ex. 41 10 4 5.532 40 1.25 2 11 Ex. 42 30 4 5.5 48 555 1.15 3 10 Ex. 43 80 4 5.5 90 951.06 5 9 Ex. 44 150 4 5.5 120 130 1.08 4 9 Ex. 45 200 4 5.5 135 150 1.114 10 Ex. 46 250 4 5.5 145 160 1.10 3 9 Ex. 47 80 1.5 5.5 62 92 1.48 −114 Ex. 48 80 2 5.5 68 93 1.37 0 13 Ex. 49 80 3.5 5.5 81 94 1.16 2 11 Ex.50 80 6 5.5 108 94 0.87 9 6 Ex. 51 80 9 5.5 135 96 0.71 13 4 Ex. 52 8012 5.5 145 96 0.66 15 3 Ex. 53 80 4 4.8 79 118 1.49 −2 15 Ex. 54 80 4 581 112 1.38 0 12 Ex. 55 80 4 5.3 85 100 1.18 2 10 Ex. 56 80 4 5.8 91 850.93 7 7 Ex. 57 80 4 6 96 77 0.80 11 5 Ex. 58 80 4 6.2 102 70 0.69 15 3

As shown in Table 3, in each of Examples 40 to 58, the sum of the amountof dishing and the amount of erosion was equal to or less than 20 nm.This indicates that a flat finished surface was obtained.

Examples 101 to 117 and Comparative Examples 101 to 110

In Examples 101 to 105 and 107 to 117, and Comparative Examples 101,102, 104, and 106 to 108, fumed silica, ortho-periodic acid, tetramethylammonium hydroxide, ethylene glycol, water, ammonium nitrate andbenzotriazole were mixed to prepare a polishing composition. In Example106, fumed silica, ortho-periodic acid, tetramethyl ammonium hydroxide,ethylene glycol, water and benzotriazole were mixed to prepare apolishing composition. In Comparative Example 103, fumed silica,tetrarnethylammonium hydroxide, ethylene glycol, water, ammonium nitrateand benzotriazole were mixed to prepare a polishing composition. InComparative Example 105, fumed silica, ortho-periodic acid, tetramethylammonium hydroxide, water and ammonium nitrate were mixed to prepare apolishing composition. In Comparative Example 106, fumed silica,ortho-periodic acid, ethylene glycol, water, ammonium nitrate andbenzotriazole were mixed to prepare a polishing composition. InComparative Example 109, ortho-periodic acid, tetramethyl ammoniumhydroxide, ethylene glycol, water, ammonium nitrate and benzotriazolewere mixed to prepare a polishing composition. In Comparative Example110, finned alumina, ortho-periodic acid, tetramethyl ammoniumhydroxide, ethylene glycol, water, ammonium nitrate and benzotriazolewere mixed to prepare a polishing compositor.

The contents of fumed silica, ortho-periodic acid, ethylene glycol,ammonium nitrate and benzotriazole in polishing compositions prepared inExamples 101 to 117 and Comparative Examples 101 to 110, and the pHs ofthe polishing compositions are shown in Table 4 below. The content oftetramethyl ammonium hydroxide in the polishing composition prepared ineach Example other than Comparative Example 106 is a content allowingthe pH of the polishing composition to have the values shown in Table 4.The average particle size D1 and the average particle size D2 of fumedsilica and fumed alumina are 30 nm and 100 nm, respectively.

Using polishing compositions prepared in Examples 101 to 117 andComparative Examples 101 to 110, the blanket wafer of tungsten waspolished for 1 minute in accordance with the polishing conditions (1)described above. The tungsten polishing rate of each polishingcomposition was determined based on the equation described above. Theresults are shown in Table 4.

Using polishing compositions prepared in Examples 101 to 117 andComparative Examples 101 to 110, the pattern wafer was polished inaccordance with the polishing conditions described above. The patternwafer was polished until the an end point was detected by an end pointdetector, i.e. a tungsten film with a thickness of 500 nm covering thesurface of the pattern wafer was completely polished. After the patternwafer was polished, the amount of erosion on an area of the patternwafer on which wiring portions exist relatively densely was measuredusing a probe profiler (HRP 340 manufactured by KLA-Tencor Co., Ltd.).The results are shown in Table 4.

TABLE 4 Ortho- Tungsten Fumed periodic Ethylene Ammonium Benzo-polishing Erosion silica acid glycol nitrate triazole rate amount (g/L)(g/L) (g/L) (g/L) (g/L) pH (Å/min) (Å) Ex. 101 50 10 0.325 10 0.175 2.23150 600 Ex. 102 100 10 0.325 10 0.175 2.2 3300 440 Ex. 103 200 10 0.32510 0.175 2.2 3400 430 Ex. 104 100 15 0.325 10 0.175 2.2 3700 560 Ex. 105100 20 0.325 10 0.175 2.2 4200 600 Ex. 106 100 10 0.325 0 0.175 2.2 1800530 Ex. 107 100 10 0.325 2.5 0.175 2.2 2500 540 Ex. 108 100 10 0.325 150.175 2.2 2800 510 Ex. 109 100 10 0.325 10 0.175 2.2 3600 490 Ex. 110100 10 0.065 10 0.035 2.2 3300 600 Ex. 111 100 10 0.195 10 0.105 2.23300 530 Ex. 112 100 10 0.65 10 0.35 2.2 3400 560 Ex. 113 100 10 1.95 101.05 2.2 3400 560 Ex. 114 100 10 3.25 10 1.75 2.2 3300 560 Ex. 115 10010 0.325 10 0.175 1.8 2600 600 Ex. 116 100 10 0.325 10 0.175 2.0 3000530 Ex. 117 100 10 0.325 10 0.175 3.0 2400 600 C. Ex. 101 10 10 0.325 100.175 2.2 2350 1000  C. Ex. 102 20 10 0.325 10 0.175 2.2 2800 800 C. Ex.103 100 0 0.325 10 0.175 2.2  650 980 C. Ex. 104 100 5 0.325 10 0.1752.2 1400 750 C. Ex. 105 100 10 0 10 0 2.2 3300 680 C. Ex. 106 100 100.325 10 0.175 1.5 2300 680 C. Ex. 107 100 10 0.325 10 0.175 4.0 1800680 C. Ex. 108 100 10 0.325 10 0.175 6.0 — — C. Ex. 109 0 10 0.325 100.175 2.2  600 550 C. Ex. 110 0 10 0.325 10 0.175 2.2 2800 1200 ^(Note1) ^(Note1): The polishing composition of Comparative Example 110further contains 100 g/L of fumed alumina.

As shown in Table 4, polishing compositions of Examples 101 to 117 hadincreased tungsten polishing rates and reduced erosion amounts. Incontrast, polishing compositions of Comparative Examples 101 and 102each containing a smaller amount of fumed silica, i.e. 20 g/liter orless, had increased erosion amounts. Polishing compositions ofComparative Examples 103 and 104 in which the content of ortho-periodicacid was 5 g/liter or less had reduced tungsten polishing rates andincreased erosion amounts. The polishing composition of comparativeExample 105 containing no ethylene glycol had an increased erosionamount. Polishing compositions of Comparative Examples 106 and 107 withthe pH of less than 1.8 or 4.0 or more had increased erosion amounts.The polishing composition of comparative Example 108 having a high pH of6.0 was incapable of polishing the blanket wafer and a pattern waferbecause they were gelated. The polishing composition of ComparativeExample 109 containing no fumed silica had a reduced tungsten polishingrate. The polishing composition of comparative Example 110 containingfumed alumina instead of fumed silica had an increased erosion amount.compositions of Comparative Examples 106 and 107 with the pH of lessthan 1.8 or 4.0 or more had increased erosion amounts. The polishingcomposition of Comparative Example 108 having a high pH of 6.0 wasincapable of polishing the blanket wafer and the pattern wafer becausethey were gelated. The polishing composition of Comparative Example 109containing no fumed silica had a reduced tungsten polishing rate. Thepolishing composition of Comparative Example 110 containing fumedalumina instead of fumed silica had an increased erosion amount.

1. A polishing composition comprising: silicon dioxide; at least onecomponent selected from periodic acids and salts thereof; at least onecomponent selected from tetraalkyl ammonium hydroxides and tetraalkylammonium chlorides; hydrochloric acid; and water, the polishingcomposition containing substantially no iron.
 2. The polishingcomposition according to claim 1, wherein the mass fraction ofhydrochloric acid in the polishing composition is 10 to 1,000 ppm. 3.The polishing composition according to claim 1, wherein the silicondioxide comprises flamed silica.
 4. The polishing composition accordingto claim 1, wherein the pH of the polishing composition is 2 to
 3. 5. Apolishing composition comprising: fumed silica at a content of greaterthan 20 g and less than or equal to 200 g per liter of the polishingcomposition; at least one component selected from periodic acids andsalts thereof at a content of greater than 5 g and less than or equal to25 g per liter of the polishing composition; a tetraalkyl ammonium saltrepresented by the following general formula (1):

 wherein R¹ represents a hydrocarbon having 1 to 4 carbon atoms, and Xrepresents a hydroxy group or a halogen atom; at least one componentselected from ethylene glycol and propylene glycol; and water, whereinthe pH of the polishing composition is greater than or equal to 1.8 andis less than 4.0.
 6. The polishing composition according to claim 5,further comprising ammoniun nitrate.
 7. The polishing compositionaccording to claim 5, further comprising at least one component selectedfrom benzotriazole and derivatives thereof.
 8. The polishing compositionaccording to claim 1, wherein the mass fractions of elements of thesecond 1:0 twelfth groups of the periodic table, aluminum, gallium,indium, thallium, tin, lead and bismuth are each 100 ppb or less.
 9. Thepolishing composition according to claim 1, wherein the polishingcomposition is used in forming a viring structure in a semiconductordevice.
 10. The polishing composition according to claim 9, wherein thepolishing composition is used in polishing a conductor layer including aconductor metal, and said conducting layer is formed on an insulatorlayer having trenches on the surface.
 11. The polishing compositionaccording to claim 10, wherein said conductor metal is tungsten.
 12. Amethod for forming a wiring structure comprising: forming a metal layerincluding a conductor layer including a conductor metal on an insulatorlayer having wenches on the surface; and forming wiring portions fromsaid conductor layer in said trenches by polishing said metal layerusing a polishing composition so that said insulator layer in areasother than said trenches is exposed, wherein said polishing compositionincludes silicon dioxide, at least one component selected from periodicacids and salts thereof at least one component selected from tetraalkylammonium hydroxides and tetraalkyl ammonium chlorides, hydrochloricacid, and water, and contains substantially no iron.
 13. A method forforming a wiring structure comprising: forming a metal layer including aconductor layer including a conductor metal on an insulator layer havingtrenches on the surface; polishing said metal layer using a polishingcomposition to remove most parts of the conductor layer outside saidtrenches, wherein said polishing composition includes silicon dioxide,at least one component selected from periodic acids and salts thereof,at least one component selected from tetraalkyl ammonium hydroxides andtetraalkyl ammonium chlorides, hydrochloric acid, and water, andcontains substantially no iron; and forming wiring portions from saidconductor layer in said trenches by polishing said metal layer usinganother polishing composition so that said insulator layer in areasother than said trenches is exposed, wherein said another polishingcomposition has a rate at which said insulator layer is polished is inthe range of 0.67 to 1.5 when the rate at which said conductor layer ispolished is
 1. 14. A method for forming a wiring structure comprising:forming a metal layer including a conductor layer including a conductormetal on an insulator layer having trenches on the surface; polishingsaid metal layer using a polishing composition to remove most parts ofthe conductor layer outside said trenches, wherein said polishingcomposition includes silicon dioxide, at least one component selectedfrom periodic acids and salts thereof, at least one component selectedfrom tetraalkyl ammonium hydroxides and tetraalkyl ammonium chlorides,hydrochloric acid, and water, and contains substantially no iron; andforming wiring portions from said conductor layer in said trenches bypolishing said metal layer using another polishing composition so thatsaid insulator layer in areas other than said trenches is exposed,wherein said another polishing composition includes silicon dioxide,periodic acid, at least one component selected from ammonia, potassiumhydroxide, sodium hydroxide, ammonium periodate, potassium periodate andsodium periodate, and water, and contains substantially no iron.
 15. Amethod for form big a wiring structure comprising: forming a metal layerincluding a conductor layer including a conductor metal on an insulatorlayer having trenches on the surface; and forming wiring portions fromsaid conductor layer in said trenches by polishing said metal layerusing a polishing composition so that said insulator layer in areasother than said trenches is exposed, wherein said polishing compositionincludes fumed silica at a content of greater than 20 g and less than orequal to 200 g per liter of the polishing composition; at least onecomponent selected from periodic acids and salts thereof, at a contentof greater than 5 g and less than or equal to 25 g per liter of thepolishing composition; a tetraalkyl ammonium salt represented by thefollowing general formula (1):

 wherein R¹ represents a hydrocarbon having 1 to 4 carbon atoms, and Xrepresents a hydroxy group or a halogen atom; at least one componentselected from ethylene glycol and propylene glycol; and water, and thepH of said polishing composition is greater than or equal to 1.8 and isless than 4.0.
 16. A method for forming a wiring structure comprising:forming a metal layer including a conductor layer including a conductormetal on an insulator layer having trenches on the surface; polishingsaid metal layer using a polishing composition to remove most parts ofthe conductor layer outside said trenches, wherein said polishingcomposition includes fumed silica at a content of greater than 20 g andless than or equal to 200 g per liter of the polishing composition; atleast one component selected from periodic acids and salts thereof, at acontent of greater than 5 g and less than or equal to 25 g per liter ofthe polishing composition; a tetraalkyl ammonium salt represent by thefollowing general formula (1):

 wherein R¹ represents a hydrocarbon having 1 to 4 carbon atoms, and Xrepresents a hydroxy group or a halogen atom; at least one componentselected from ethylene glycol and propylene glycol; and water, and thepH of said polishing composition is greater than or equal to 1.8 and isless than 4.0; and forming wiring portions from said conductor layer insaid trenches by polishing said metal layer using another polishingcomposition so that said insulator layer in areas other than saidwenches is exposed, wherein said another polishing composition has arate at which said insulator layer is polished is in the range of 0.67to 1.5 when the rate at which said conductor layer is polished is
 1. 17.A method for forming a wiring structure comprising: forming a metallayer including a conductor layer including a conductor metal on aninsulator layer having trenches on the surface; polishing said metallayer using a polishing composition to remove most parts of theconductor layer outside said trenches, wherein said polishingcomposition includes fumed silica at a content of greater than 20 andless than or equal to 200 g per liter of the polishing composition, atleast one component selected from periodic acids and salts thereof at acontent of greater than 5 g and less than or equal to 25 g per liter ofthe polishing composition, a tetraalkyl ammonium salt represented by thefollowing general formula (1):

 wherein R¹ represents a hydrocarbon having 1 to4 carbon atoms, and Xrepresents a hydroxy group or a halogen atom; at least one componentselected from ethylene glycol and propylene glycol; and water, and thepH of said polishing composition is greater than or equal to 1.8 and isless than4.0; and forming wiring portions from said conductor layer insaid trenches by polishing said metal layer using another polishingcomposition so that said insulator layer in areas other than saidtrenches is exposed, wherein said another polishing composition includessilicon dioxide, periodic acid, at least one component selected fromammonia, potassium hydroxide, sodium hydroxide, ammonium periodate,potassium periodate and sodium periodate, and water, and containssubstantially no iron.
 18. The method for forming a wiring structureaccording to claim 12, wherein said conductor metal is tungsten.